Loss experiences are associated with increased morbidity and mortality and risk for affective disorders both at the time of the loss and at later dates. Most research in psychoneuroimmunology has focused on the acute and immediate effects of stressor exposure. The present project will continue the evaluation of the acute effects of brief maternal separation experiences in nonhuman primates on behavior and immunoregulation in addition to a more detailed focus on the long term consequences of such experiences. An extensive literature suggests that early social experiences may have behavioral and endocrine effects in the adult ranging from subtle to quite severe. Our preliminary studies of brief maternal separation experiences suggest that long term consequences are species dependent, which are likely a function of different patterns of maternal and allomaternal care. We view this as an animal model of social support. The present study will investigate the relationship between mother-infant interactions and behavior of the juvenile in a number of novel stressor experiences in addition to a characterization of immunoregulation. This prospective project will also permit the description of puberty onset as influenced by early separation. Immunoregulation will be evaluated through several in vitro measurements, the assessment of in vivo responses (specific antibody production to novel antigens), and measurement of IL-2 as a first approximation toward the localization of a means through which the immune responses have been modulated. This project has implications for the acute consequences of loss experiences in HIV+ populations, which are extraordinary high among HIV+ gay populations. Furthermore, it has relevance for HIV infected individuals who experienced significant losses during development, perhaps subsequently placing them at a greater risk for progression of illness during stressor exposure.